Ring Constraint Strategy Enabled Cycloaddition of Oxazolones and Alkenes via Photoinduced Energy Transfer

2-Aminocyclobutanols are important motifs found in natural product synthesis and pharmaceuticals. Although their synthesis has been reported by modification of cyclobutanes, sustainable methods for polysubstituted 2-aminocyclobutanols remain underdeveloped due to challenges with reactivity and selectivity. In this work, we introduce a visible-light-mediated intermolecular [2 + 2] photocycloaddition for producing polysubstituted 2-aminocyclobutanols. By leveraging triplet energy transfer, oxazolones undergo [2 + 2] cycloaddition with various alkenes, both activated and unactivated. This approach is notable for its simplicity, mild conditions, broad substrate scope, and high regio- and diastereoselectivity, enabling complex molecule synthesis from readily available materials. Additionally, we also demonstrate a highly unusual cycloaddition with vinylcyclopropanes to construct [6,5]-fused scaffolds. Finally, mechanistic studies are included, revealing that cycloaddition is achieved through the radical addition of excited state oxazolones to alkenes, followed by radical-radical recombination.